There is a list on chinuch.org that has a list of kosher titles for kids, complete with the reasons why books would be yes or no.
also, whoever it was that said Jodi Picoult- she is an excellent writer, but I wouldn’t call her books “Kosher”, she sticks at least one unnecessary romance in each book and then proceeds to make a few graphic scenes out of it. The only way these books are Kosher is if you have them censored.